A fuel injection system in a diesel engine is generally made up of a jerk type fuel injection pump such as a distributor pump or an in-line pump and fuel injection nozzles.
The fuel injection nozzles are means for supplying fuel in an atomized state to the cylinders of the engine, and as disclosed for example in Japanese Unexamined Patent Publication No. S.59-180063 may have a construction wherein a needle valve is received in a nozzle body slidably in the axial direction of the needle valve and the nozzle body and this needle valve is urged closed from the axial direction rear thereof by a spring and the needle valve has a conical pressure-receiving surface at its tip and by a fuel pressure sent out from a jerk type fuel injection pump being made to act on this pressure-receiving surface the needle valve is opened and fuel is injected into a combustion chamber of the engine through a plurality of nozzle holes formed in the tip of the nozzle body.
However, with this construction, the fuel injection pressure, the injected amount and the injection speed are generally determined by the characteristics and the capacity of the jerk type fuel injection pump, and furthermore it is not possible to finely increase or decrease the total nozzle hole area. Consequently, during low-speed running of the engine the fuel injection pressure decreases and during low-load running of the engine the injection time becomes short and it is not possible to maintain a good combustion state, and it has been difficult to promote fuel combustion and achieve improvements in output and fuel consumption and reductions in combustion noise and NOx emissions.
As a measure to overcome this, in Japanese Unexamined Patent Publication No. H.4-76266, a fuel injection nozzle having a variable nozzle hole area has been proposed. In this related art, a plurality of nozzle holes are formed spaced in the circumferential direction in a wall bounding a well formed in the tip of the nozzle body and a rotatable shaft to serve as a rotary valve is passed through the center of the needle valve and has its tip positioned in the well. Passages are provided in the tip of the rotary valve shaft and a fuel pressure chamber in the well and the nozzle holes are connected by these passages when the needle valve opens.
However, this related art only provides control setting the rotary valve to a position such that four nozzle holes are open at times of low-speed and low-load running of the engine and switching the position of the rotary valve to a position such that eight nozzle holes are used at times of high-speed/high-load running; that is, the method merely consists of switching the number of open nozzle holes between four and eight and does not allow the nozzle hole area to be finely adjusted to a nozzle hole area optimal to the running state of the engine. Also, there is the problem that when the number of open nozzle holes is switched, the spray direction also changes.
Furthermore, in this related art, there is no disclosure relating to how to control the rotary valve to obtain an optimum nozzle hole area. In particular, when a variable nozzle hole type fuel injection nozzle is combined with a jerk type fuel injection pump, to optimize the nozzle hole area it is necessary to control the angle of the rotary valve taking into account the speed of the jerk type fuel injection pump, the responsiveness and rotating torque of an actuator rotating the rotary valve, and because in the related art there has been no disclosure providing means or methods for solving these problems this kind of pump-nozzle combination has up to now been lacking in practicality.